Data Matrix is the 2D barcode of industry: on electronic parts, medicine packs, surgical instruments - often printed or engraved very small. With GS1 data it's GS1 DataMatrix, the one on medicines in Europe and on more and more products.

Square (Size Auto)

Rectangular (16x48)

What it holds
Characters	Letters, digits and symbols, and the accented letters of Western European languages - é, ü, ñ and the like. The euro sign, other alphabets and emoji don't fit: use a QR Code for those.
Length	Up to 3,116 digits, 2,336 letters, or about 1,550 characters of mixed text.
Error correction	Built in, and set by the size: there's nothing to choose.
Readable text	None.

Settings
Size	Automatic size picks the smallest square the value fits, from 10x10 to 144x144 modules. A fixed size keeps every label alike: when the value doesn't fit it, Labeljoy uses a bigger one - a square, if you chose a square. The rectangles, 8x18 to 16x48, are used only when you choose one: they fit a narrow space, but not every scanner reads them.
Encoding	Standard, GS1 or HIBC: see GS1 and HIBC data.

Characters you can't type. With Encoding set to Standard, a tilde followed by three digits is the character with that code - ~013 is a carriage return - and ~~ is a tilde.

The rest of the settings - quiet zone, color - are in the Barcode section.

What goes wrong
Input data is too long to fit into the symbol.	The value doesn't fit even the largest Data Matrix.
Only Latin-1 characters, the letters of Western European languages, fit in this barcode.	The value has a character Data Matrix can't hold - a euro sign, another alphabet, an emoji.